On Thu, Mar 25, 2021 at 11:52:29AM -0700, Junio C Hamano wrote: > Junio C Hamano <gitster@xxxxxxxxx> writes: > > >> So, I'm of two minds here: > >> > >> 1. This is embarassing. I wasted everyone's time for nothing. I can retract > >> this patch. > >> > >> 2. This is embarassing. I overstated the problem here. But we might be able > >> to eke out a tiny performance boost here. > >> > >> I'm open to either. I think we should default to dropping this patch unless > >> someone thinks the rewrite above is a better organization of the logic. (I > >> can then send a v2 including that version and an updated commit message.) > > > > 3. The current code around "if (nr == sizeof(f->buffer))" might be a > > bit too clever for readers who try to understand what is going > > on, and the whole "while" loop may deserve a comment based on > > what you wrote before your replacement implementation. Yes, my first thought on reading Stolee's post-image was: wait, how do we know when data needed flushed from the buffer? But that is not new in his patch. It is confusing before and after. :) > Having said all that, comparing the original and the version updated > with your "flush less often" patch, I find the latter quite easier > to read, so as long as the update does not give us 1% slowdown, it > may be worth adopting for the readability improvement alone. > > Of course, if we were to go that route, the sales pitch in the log > message needs to be updated. Yeah, I am OK with either version, as long as it is justified correctly in the commit message. IMHO the big difference is that the original is using local data/offset variables in order to provide a layer of indirection when we get to the hash+flush code. And Stolee's patch is calling the same code in the two places instead. It's quite possible that gives the compiler slightly more opportunity to micro-optimize (which doesn't matter if you are feeding big blocks, but may if you are feeding 4 bytes at a time as in the midx code; though in that case it is entirely possible that the caller allocating a single array, writing it, and then feeding it to hashwrite() would be faster still, though a little more cumbersome). -Peff
